I would not say that all slip in cams are not up to the task Look at the Kury 26 cam its works under a stock head , yet install this slip in cam with heads and increased compression and it will pull into the 6500 RPM range... Many of the woods cams fall into this as well, Fueling 574 cam is a great bolt in cam , add some head work and it only gets better.. Many times the heads can be the stopping point on many of the builds not the slip in cams.. The cam has much more to offer yet other items are holding it back. Its all about the combo .
But opinions are what they.. " some say if it cost's more it must be better" Curtis Hamliton..
Not trying to get into a pissing match but some enjoy taking the stab every chance they get.. Being that we have installed a fair amount of these cams tuned them, added pistons, along with head work and have seen what they can offer.. Take a look at the money invested to gain that little bit more.. Tq wise the gains are small ,..hp the gains are bigger however the next question is how often is the engine at 6000 RPM and it is only there for a few tenths of a second..